Abrasive tool containing coated superabrasive grain

Abstract

An abrasive grit for a metal bonded Single Layer abrasive tool includes abrasive grains coated with a first active component. The active component is mechanically-bound to the surface of the superabrasive grains. Preferably the abrasive is a superabrasive, especially diamond, and the first active component is titanium, either in the form of elemental Ti or TiH 2 . The novel grit is made by mixing the first active powder component in a liquid binder to form an adhesive paste; mixing the paste with the abrasive grains to wet the grains, and drying the mixture to adhere active component to the grains. The coated abrasive can be brazed onto a core to form a Single Layer tool, especially with a brazing composition that includes a bronze alloy and small concentrations of a second active component. During brazing the novel abrasive grains provide excellent surface contact with the brazing composition and the braze strongly bind the grains to the tool core. The brazed composition is easy to chemically or electrochemically strip from the cores of worn abrasive tools to permit reconstruction of the tools.

We claim: 
     
       1. A process for making an abrasive tool having a metal core comprising the steps of: (A) mixing to a uniform composition a first active powder component and an effective amount of a liquid binder to form an adhesive paste;   (B) mixing superabrasive grains, each having a surface area, with an effective amount of the adhesive paste to wet a major fraction of the surface area of the superabrasive grains with the paste;   (C) drying the liquid binder thereby producing coated superabrasive grains having a mechanically bound surface coating >1 micron in thickness of the first active powder component;   (D) coating an operative surface of the core with an effective amount of a brazing composition comprising a second active component;   (E) depositing a single layer of coated superabrasive grains into the brazing composition on the operative surface of the metal core;   (F) heating the coated metal core under an inert atmosphere to remove substantially all liquid binder; and   (G) brazing the coated superabrasive grains to the core at a temperature of at least 700° C. to effect a reaction between the superabrasive grains, the first active component and the second active component.   
     
     
       2. The invention of claim 1 wherein the coated superabrasive grains have a surface coating of about 4 to 150 microns in thickness of the first active powder component. 
     
     
       3. The invention of claim 1 wherein the first active powder component has a particle size of about 4 to 44 μm. 
     
     
       4. The invention of claim 1 wherein the superabrasive is selected from the group consisting of diamond and cubic boron nitride. 
     
     
       5. The invention of claim 1 wherein the second active component is present in the brazing composition in the form of a powder of particle size in the range of about 4 to about 150 μm. 
     
     
       6. The invention of claim 1 wherein the first active component comprises a metal selected from the group consisting of titanium, silicon, chromium, tungsten, vanadium, molybdenum, hafnium, iron, zirconium, and reactive compounds thereof and mixtures thereof. 
     
     
       7. The invention of claim 6 wherein the first active component is selected from the group consisting of elemental titanium and titanium hydride. 
     
     
       8. The invention of claim 1 wherein the second active component comprises a metal selected from the group consisting of titanium, silicon, chromium, tungsten, vanadium, molybdenum, hafnium, iron, zirconium, and reactive compounds thereof and mixtures thereof. 
     
     
       9. The invention of claim 8 wherein the second active component is selected from the group consisting of elemental titanium and titanium hydride. 
     
     
       10. The invention of claim 1 wherein the drying step includes heating the coated superabrasive grains to about 50° C.-300° C. until the liquid in the binder evaporates. 
     
     
       11. The invention of claim 1 wherein the brazing composition comprises (1) 100 parts by weight of a coarse powder of a bronze alloy consisting essentially of about 10-30 wt % tin and a complementary amount of copper;   (2) about 0.5-7 parts by weight coarse powder of a second active component; and   (3) about 15-30 parts by weight of a liquid vehicle.   
     
     
       12. The invention of claim 11 wherein the total of first active component and second active component is less than about 5 parts by weight per 100 parts by weight of bronze alloy. 
     
     
       13. The invention of claim 11 wherein the second active component is about 0.5 to 3.0 parts by weight per 100 parts by weight of bronze alloy. 
     
     
       14. The invention of claim 11, wherein the brazing is carried out by heating the coated metal core to a temperature of 750° to 950° C. for 5 to 30 minutes under a non-oxidizing atmosphere.